Oscillatory circuit



J. N. WHITAKER 2,067,365

05 CILLATORY C IRCUIT Jan. 12, 1937 2 Sheets-Sheet 2 Filed March 19, 1932 I I I I I IH INVENTOR JAMES N. WHITAKER ATTORNEY Patented Jan. 12, 1937 OSCILLATORY CIRCUIT James N. Whitaker, Tuckahoe, N. Y., assignor to Radio Corporation of America, a corporation of Delaware This invention relates broadly to the frequency generation and stabilization of alternating currents either of audio frequencies or, and especially, currents of radio frequencies.

Heretofore it has been customary to utilize for the production of oscillations, some form. of master oscillator followed by buffer amplifiers and then frequency multipliers. The burer amplifiers tended to prevent reaction of the load upon the master oscillator, and, the frequency multipliers were made separate and apart from the master oscillator. An object of my present invention is to simplify such a system, and to do so I have devised an arrangement whereby the buffer amplifiers and. their accompanying evils such as increased. cost of maintenance are eliminated. A further advantage of my present system resides in the fact that the number of frequency multipliers necessary to obtain a desired frequency is reduced which also lessens maintenance cost as well as lessening the liability of shut down as compared to a system wherein more units or electron discharge devices are required.

My present invention is more fully described in connection with the. accompanying drawings, wherein,

Fig. 1 illustrates a system which, according to my present invention, utilizes an electron discharge device so biased as to have a negative resistance characteristic, output circuits of the device being tuned to successively higher harmonic frequencies or" a frequency stabilizing system associated with the input electrodes of the device,

Fig. 1a diagrammatically indicates any source of constant frequency potential such as a vacuum tube oscillation generator or tuning fork controlled oscillation generator which may replace, for example, the crystal 2 of Figure 1.

Fig. 2 illustrates a modification wherein the negative resistance characteristic of the system shown in Fig. 1 is no longer made use of, and in particular illustrates a system for obtaining by means of a pentode tube, a high frequency from a relatively low constant frequency controlling apparatus, and,

Figs. 3 and 4 are modifications of the preferred form of my invention illustrated in Fig. 1.

Turning to Fig. 1, a piezo-electric crystal 2 is; connected between the control electrode or grid 4 and cathode or filament 6 of electron discharge device 8, preferably a high vacuum tube. Control grid bias is maintained by the action of choke coil Ill-polarizing battery 22 combination connected between the grid and cathode, although of course any other form of biasing means such as a grid leak resistorcondenser combination may be used. The screen grid it is connected through a parallel tuned circuit it to a source of potential 26 as is also the anode 22 through another parallel tuned circuit 2%. Preferably, as illustrated, the screen grid i6 is maintained at a higher positive potential than the anode 22, the potentials chosen being such that the electron discharge device 8 has a negative resistance characteristic. Consequently, by the insertion of a resonant system such as 25 in the anode circuit, the system will generate oscillations at a frequency roughly determined by circuit 2 3.

However, to maintain the frequency of oscillations generated constant, I connect across the grid filament circuit at points A and B a frequency controlling system here shown in the form of piezo-electric crystal 2. The frequency of the piezo-electric crystal 2 is chosen such that it is a proper sub-multiple of a desired frequency, or rather, circuit Z lis tuned to some harmonic of piezo-electric crystal 2. With this system, it will be found that the oscillations generated by the negative resistance characteristic, or better known dynatron characteristic of the tube 8 will be locked or pulled into step with the constant frequency oscillations of the piezo-electric crystal 2 such that the oscillations in circuit 24 are always built up at the harmonic frequency to which it is tuned.

In the event that it is desired to have, say, the fourth harmonic appear in circuit 24, it is preferable that parallel tuned circuit 58 be tuned to the second harmonic, for, by analyzing the relative phases of the oscillatory currents flowing through the various circuits it will be found that they are in correct relation for producing in circuit 24 a fourth harmonic. Also, the relative phases will be found correct for other harmonics such as obtainable, for example, by tuning circuit l to the third harmonic and 2a to the ninth.

While oscillations are generated in circuit 72 i by dynatron or negative resistance characteristic action of electron discharge device 8 they are generated in circuit l8 by virtue of regenerative action, capacitive feed back occurring between the screen grid i6 and the control grid :3 within the tube. If desired this capacitive feed back may be augmented by connecting a small condenser across the screen grid I6 and control grid 4.

Moreover, if desired, circuit 48 may be tuned to the fundamental or natural frequency of pi ezo-electric crystal 2, or, the circuit l8 may be replaced by a simple inductance coil whose natural frequency is higher than the frequency of piezo-electric crystal 2.

It will be found that with the system as described, a considerable amount of power will be available from this form of oscillatory system and this together with the frequency multiplication and will give the equivalent of the heretofore necessary master oscillator, buffer amplifier and frequency multiplier combinations. Moreover, it will be found that even with the circuit 2 2 completely short circuited, there will be no reaction upon the frequency controlling system 2, which of course is a prime desideratum in alternating current generating systems.

Moreover, it should be clearly understood that though preferable piezo-electric crystal need not be connected across points A and B. As illustrated in Fig. la, any form of generator such as a vacuum tube generator or tuning fork controlled vacuum tube generator may be connected across points A and B. Or, more simply, a simple parallel tuned circuit may be connected across points A and B in which case the biasing system consisting of condenser as and leak resistor it of Fig. 3 is used.

Also, in the system shown in Fig. 1, the filament 6 is grounded as illustrated, and, the lower ends of the circuits i3, 25 are grounded by the action of by-passing condensers 25 to prevent the flow of high frequency currents to the source 20.

Output energy may be taken from circuit 24 through blocking condenser 23 and fed, if desired, to a power amplifier 3i! and then radiatedv over a suitable radiating antenna 32. For Signalling purposes modulation may be accomplished by placing a resistor 3 3 in series with the anode, and varying the current flow therethrough by means of electron discharge device 36. connected, as shown, with manipulation of key 38.

Current flow through tube 35 corresponding to the lower position of key 38, will lessen the voltage on anode 22 to such an extent that there is a material decrease and if desired absolute absence of oscillatory energy in circuit 24. On the other hand, connecting key 38 to the upper position or tap will cause tube 35 to block as a result of which suflicient anode potential will reach anode 22 to allow oscillatory energy to enter power amplifier 30. Also, it is to be understood that keying arrangement 38 may be replaced by a microphone and battery or by any suitable audio or other modulating frequency source.

Also, if desired, fundamental or harmonic frequency energy may be taken. from parallel tuned circuit [8 as illustrated and fed to a buffer amplifier BA the output of which is modulated by a suitable modulator M. The modulated output may then be fed to a power amplifier PA and then radiated over a transmitting antenna TA, or, may be sent over wire lines if desired.

In the arrangement shown in Fig. 2 wherein.

the tube 8 is of the pentode type, having a screening electrode ii! adjacent the anode 22 to prevent secondary emission, the action of the system is changed in that no oscillations are present unless some form of oscillatory system. is connected across the points A B. It will be remembered that in connection with Fig. 1 oscillations are present in the anode output circuit 2 5, and are frequency stabilized by the connection of a pieZo-electric crystal, a parallel tuned siderable feed back between the screen grid [8 1' and the control grid 4, no oscillations will be present in the anode circuit 24 or screen grid circuit it. In other words, the negative resistance or dynatron action is sacrificed by utilizing the fifth electrode it.

In the circuit shown in Fig. 2 circuit It may be tuned to, some fundamental frequency or some harmonic frequency of the system connected across points A and B. Circuit may be tuned to the same harmonic or to a higher harmonic relative to the tuning of circuit l8. Or, circuit 2 5 may be tuned to the fundamental if desired. However, I prefer to tune circuit 18 to, for example, the first even or odd harmonic and, circuit 2% to a still higher harmonic. Oscillations of harmonic frequency occur in circuit is because of regenerative action between electrodes IE, 1 and the cathode 6, and, harmonic frequency oscillations appear in circuit 2 3 by virtue of the frequency multiplying action of tube 3.

In Fig. 2, if desired, the anode 22 is maintained at 'a suitable potential relative to the screen grid it.

As in Fig. 1, the arrangement illustrated in Fig. 3

lower than the screen grid it giving rise to dynatron or negative resistance action such that oscillations are set up in the anode circuit 2 of a desired frequency. The screen grid $5,, control grid and cathode S, are connectedtoa parallel tuned circuit 32 in Fig. 3 such that the screen grid and control grid wobble oppositely in phase as a result of which due to regenerative action oscillations are set up in circuit 42, screen grid i5 acting as a plate relative to the control grid i and cathode 6. The oscillations in circuit A; which may be harmonically related in frequency to the oscillations in circuit 42, are then looked into step with the oscillations in circuit @2, the circuit having the advantage that there is a minimum of reaction between the load circuit or anode circuit 24% and the frequency controlling circuit 42.

In the arrangement shown in Fig. 3 condenser 2% and resistance 45 act as a condenser grid;

leak resistor combination for maintaining suitable bias upon the control grid 5, and, condensers 2 8 are the usual blocking or radio frequency by passing condensers.

In order to modulate the output of tube 8, constant current may be supplied through choke coil as and a portion thereof diverted by means of modulator tube 52 in accordance with voice potentials from microphone 53 as illustratedutilizes a screen grid tube 8 in which the anode is maintained at a potential substantiallycaded arrangement such that for example the output is fed into points corresponding to points A and B of a succeeding tube. The succeeding tube or tubes may then be tuned to still higher harmonics to derive still higher frequencies as will be apparent to those skilled in the art after a reading of the present specification.

Moreover, if desired, pushpull arrangements of the various forms of my invention may be utilized. An example of that type of circuit is i1-" lustrated in Fig. 4 wherein tubes 8 have their screen grids l6 maintained at a higher positive potential relative to voltage on the anodes 22. Some form of frequency controlling system such as a piezo-electrio crystal 2 is connected between the control grids 4 bias for which is supplied by means of biasing battery i2 through the divided resistor 54. The screen grid parallel tuned circuit may be simply an inductance coil or preferably a parallel tuned circuit 56 tuned to either the fundamental or a low harmonic of the natural frequency of the resonant system 2. The anodes are interconnected by means of a second parallel tuned circuit 58 tuned to preferably, some multiple of the frequency of the resonant system 2 and preferably tuned to a higher frequency than circuit 56. oscillatory energy by virtue of the negative resistance characteristic of the tubes 8 will then, of course, be set up in the parallel tuned circuit 58 and be frequency stabilized by the controlling action of the resonant system 2, forming part of a regenerative oscillating system comprising the filaments, the control grids and the screen grids of tubes 8.

Although reference has been made in general to harmonically related frequency outputs, it is to be clearly understood that the systems may have outputs, if desired, of sub-harmonic frequencies relative to the controlling frequencies. In such cases, circuits 24 of Figs. 1, 2 and 3 and circuit 58 of Fig. 4 are preferably resonated to the desired sub-harmonic frequency.

Modulation of the output appearing in parallel tuned circuit 58 may be accomplished by superimposing modulating potentials upon the anodes by means of transformer 68. Modulated energy may then be power amplified by power amplifier 62 and fed to a suitable radiating antenna 6 3 for signaling purposes.

The output energy of my systems may, of course, be used in various other ways as, for example, in heterodyne receivers, or, for frequency measuring purposes as will be evident to those skilled in the art. Moreover, various other 2 changes may be made in my present invention without departing from the scope thereof and accordingly my present invention is not to be limited by the exact embodiments described, but rather by the breadth of the appended claims:

Having thus described my invention, what I claim is:

1. In a system for producing oscillations of constant frequency, a multi-electrode device having an anode, a cathode, a screen grid, and a control grid; a circuit coupled to said anode and cathode, means for polarizing said anode to a positive potential relative to said cathode, means for polarizing said screen grid to a higher positive potential relative to said cathode whereby oscillations are set up in said circuit coupled to said anode and cathode due to the negative resistance characteristic of said device; an oscillatory system coupled to said control grid and cathode for stabilizing the frequency of oscillations in said circuit coupled to said anode and cathode and an oscillatory circuit coupled between said screen grid and cathode and tuned to a frequency bearing a harmonic relation to the frequency of oscillations in said control grid circuit.

2. A system for producing constant frequency comprising an. electron discharge device having an anode, a cathode, a screen grid and a control grid, means for polarizing said anode to alower positive potential with respect to said screen grid to give said device a negative resistance characteristic, a resonant circuit connected between said anode and cathode whereby oscillations are set up therein due to the negative resistance characteristic of said device, and, means for subjecting said control grid and cathode to constant frequency oscillations different from but bearing a harmonic relation to the frequency of oscillations in said anode circuit whereby the oscillations in the anode circuit are stabilized in frequency in accordance with the potentials to which said control grid and cathode are subjected.

3. A system for producing constant frequency oscillations comprising an electron discharge device having an anode, a cathode, a control grid and a screen grid, means for polarizing said screen grid at a positive potential relative to said cathode, means for polarizing said anode at a lesser positive potential relative to said anode thereby giving said device a negative resistance characteristic, a parallel tuned circuit connected between said anode and cathode, a parallel tuned circuit connected between said screen grid and cathode, and a piezo-electric crystal connected between said control grid and cathode, said parallel tuned circuit connected between said anode and cathode being tuned to a frequency bearnig a harmonic relation to a natural frequency of said piezo-electric crystal.

l. Apparatus as claimed in the preceding claim wherein said parallel tuned circuit connected between said screen grid and cathode is tuned to a harmonically related frequency relative to the frequency of said piezo-electric crystal and wherein said parallel tuned circuit connected to said anode is also tuned to a harmonica ly' related frequency.

5. In apparatus'of the character described, an electron discharge device having an anode, a cathode, a grid adjacent said cathode, and a grid intermediate said adjacent grid and said anode, an oscillatory system connected between the grid adjacent said cathode and said cathode, an oscillatory system tuned to a higher harmonic frequency than said first mentioned oscillatory system connected between said intermediate grid and said cathode, and, an oscillatory system connected between said anode and cathode, said last mentioned oscillatory system being tuned to a still higher harmonic frequency than either of the two oscillatory systems first mentioned.

6. An oscillatory system comprising an electron discharge device having an anode, a cathode, a screen grid and a control grid, means for regeneratively connecting together said screen grid, control grid, and cathode whereby oscillations are generated by virtue of said regenerative connecting means, a tuned circuit connected to said anode, means for subjecting said anode to a substantially lower unidirectionally positive potential with respect to the cathode than the positive potential to which said screen grid is subjected, whereby oscillations are set up in said tuned anode circuit by virtue of negative resistance action, and whereby said last mentioned oscillations set up by negative resistance action are locked into step at constant frequency with the oscillations generated by regenerative action.

7. An oscillatory system comprising an electron discharge device having an anode, a cathode, a screen grid and a control grid, means for polarizing said anode to a lower positive potential with respect to said screen grid to give said device a negative resistance characteristic, a resonant circuit connected between said anode and cathode whereby oscillations are set up therein due to the negative resistance characteristic of said device, and, means for subjecting said control grid and cathode to constant frequency. oscillations bearing a sub-multiple relation to the frequency of oscillations in said anode circuit whereby the oscillations in the anode circuit are stabilized in frequency in accordance with the potentials to which said control grid and cathode are subjected.

8. A system for producing constant frequency oscillations comprising an electron discharge device having an anode, a cathode, a control grid and a screen grid, means for polarizing saidv screen grid at a positive potential relative to said cathode, means for polarizing said anode at a lesser positive potential relative to said cathode thereby giving said device a negative resistance characteristic, a parallel tuned circuit connected between said anode and cathode, a parallel tuned circuit connected between said screen grid and cathode, and a piezo-electric crystal connected between said control grid and cathode, said parallel tuned circuit connected between said anode and cathode being tuned to a frequency bearing a sub-harmonic relation to a natural frequency of said piezo-electric crystal.

9. In apparatus of the character described, an electron discharge device having an anode, a cathode, a grid adjacent said cathode, and a grid intermediate said adjacent grid and said anode, an oscillatory system connected between the grid adjacent said cathode and said cathode, an oscillatory system tuned to a lower harmonic frequency than said first mentioned oscillatory system connected between said intermediate grid and said cathode, and, an oscillatory system connected between said anode and cathode, said last mentioned oscillatory system being tuned to a still lower harmonic frequency than either of said oscillatory systems heretofore referred to.

10. An oscillatory system comprising an electron discharge device having an anode, a cathode, a control grid and a screen grid, a piezoelectric crystal connected between said control grid and cathode, a parallel tuned circuit connected between said screen grid and cathode, and a parallel tuned circuit connected between said anode and cathode, said last mentioned parallel tuned circuit being tunedto a sub-harmonic of said piezo-electric crystal frequency.

11. An oscillation generation system comprising a pair of push-pull connected electron discharge devices, each device having an anode, a cathode, a screen grid, and a control grid, an oscillatory system connected between the control grids of said two devices, a parallel tuned oscillatory circuit connected between the screen grids of said two devices, and a parallel tuned oscillatory circuit connected between the anodes of said two devices, said two parallel tuned circuits being tuned to a frequency bearing a harmonic relation to the, frequency of oscillations in the oscillatory system connected to said control grid.

12. A system in accordance with claim 11, characterized in this, that said oscillatory system connected between the control grids of said two devices comprises a piezo-electric crystal having in shunt across said crystal means for biasing both of said control grids.

13. An oscillatory system comprising an electron discharge device having a cathode, a control grid, a screen grid, a suppressor grid and an anode, a piezo-electric device connected between the cathode and control grid, a parallel tuned circuit connected between the cathode and screen grid, a second parallel tuned circuit connected between the cathode and anode and tuned to a frequency harmonically related to a natural frequency of said piezo-electric device, means for so polarizing said suppressor grid with respect to said screen grid and said anode that secondary emission from said anode is prevented, means for producing a regenerative action between the screen grid circuit and the control grid circuit, and means for causing a frequency multiplier action to take place in the anode circuit.

14. An oscillation generator and frequency multiplier comprising an electron discharge tube having a cathode, an anode and at least two intervening grid electrodes, means for applying across the anode, cathode, and grid adjacent the anode, of said tube uni-directional potentials of such values that between the cathode and anode a negative resistance characteristic is developed, a source of control frequency connected between the cathode and the grid electrode adjacent thereto, and a resonant tank circuit connected between the anode and cathode and tuned to a frequency harmonically related to said control frequency.

JAMES N. WHITAKER. 

